Cloud services have become an available and affordable data storage service. A typical service offered by a cloud storage provider is an object storage service. Object storage services generally charge a small transaction fee to write and read data as well as a fee for the amount of data stored. Object storage services typically utilize multiple replicas to guard against data loss to increase reliability. Object storage services are often accessed through Internet Protocol methods. Objects are written to the object store similar to a file system in that when an object is written to the object storage service, the object is an accessible entity. The whole object is written as part of a single command, and retrieved as a single command.
For backup operations of larger volumes, the initial backup operation of an entire storage system may prove to be a bottleneck. This may be due to the sheer size of the volume and available connection bandwidth, and in some situations may take weeks or months to complete using online bandwidth. To address this concern, some cloud services offer a bulk storage device backup option that allows the storage system to transfer the volume to the bulk storage device(s) and then ship those devices to the cloud services' physical location, where the volume is transferred from the bulk storage device(s) to the cloud service, which may take fewer time than transferring the volume online.
Problems can arise, however, while the bulk storage device(s) is in transit to the cloud service. For example, if the storage system is kept offline during this time, there is significant interruption to the storage system's operations. If the storage system is kept online, however, problems arise with how to maintain data consistency between what is backed up to the cloud service and any changes that may occur to data in the impacted volume(s) due to input/output (I/O) operations that come from one or more hosts during this time frame. Further, the storage system has an interest in confirming that data integrity has been maintained for the volume during the bulk transfer (e.g., no data from the volume is permanently lost from the cloud backup due to failure of a physical device, etc. during the transfer).